Goals of this project are to understand the structures and functions of membrane glycoproteins in normal and abnormal erythropoiesis. Research is conducted on normal erythroblasts and specific erythroid maturation stages as well as preleukemic and terminal leukemic erythroblasts obtained from avian erythroblastosis virus (AEV) and avian leukosis virus (ALV) infected chickens. These two forms of erythroleukemia offer a unique comparison, since cells transformed by AEV involve the viral oncogene sequences v-erb A and B, and the slowly developing erythroleukemia resulting from infection by the non-oncogene-carrying ALV involves the expression of the cellular protooncogene, c-erb B. Research involves the use of: (1)\a panel of monoclonal and polyclonal antibodies to erythroid developmental and differentiation-related membrane antigens; (2)\erythroleukemiaassociated antigens including the v-erb-A cell membrane product and epidermal growth factor receptor that exhibits extensive homology with the membrane glycoprotein coded for by v-erb-B; (3)\transferrin receptor; (4)\chicken major histocompatibility class I, B-F, antigens, and unique chicken erythroid-specific B-G major histocompatibility antigens; (5)\cell fractionization procedures; and (6)\cell-surface labeling techniques. Current studies show: (1)\preleukemic, terminal leukemic, and in vitro cultured leukemic cells differ in cell-surface antigen expression; (2)\expression of an antigen on preleukemic ALV-transformed cells that reacts with antisera to the epidermal growth factor receptor; and (3)\characterization of two potential erythroid growth/differentiation-related molecules. Why tumor cells do not differentiate and factors that promote unrestricted division and growth are particular areas of our interest. (AG)